1. Field of the Invention
The invention is generally related to the area of audio technologies. In particular, the invention is related to method and apparatus for automatically enabling a subwoofer channel output based on automatic detection of one or more subwoofer devices.
2. The Background of Related Art
A conventional stereo audio player usually contains an amplifier to power a set of speakers. A typical amplifier is configured for a predetermined set of channels, for example, three channels (i.e., left, right and subwoofer). The stereo audio player receives audio sources as an input, converts the input to analog audio signals that are then amplified in one or more amplifiers to drive the speakers so as to reproduce audio sounds. In general, primary configurations for an audio player may include a 2-channel, 3-channel or 6-channel connection.
1) 2-channel: the stereo audio player is connected to two speakers: left and right speakers to form a stereo sound;
2) 3-channel (or 2.1 sound effects): the stereo audio player is connected to three speakers: left and right speakers and a subwoofer to form a stereo sound; and
3) 6-channel (or 5.1 sound effects): the stereo audio player is connected to five speakers: front left, front right, center, rear left and rear right speakers and a subwoofer to form a surrounding sound.
Subwoofer is a loudspeaker that is capable of reproducing audio sound in bass or low frequencies. The audio source input to an audio player may be in different sound effect configurations, for example, 2-channel or 3-channel. If the audio source input matches the output speaker configuration, the analog output audio signal will be played properly at each corresponding speaker. In the case where the input and output configuration mismatch, the audio player may not reproduce the audio properly if the audio player is not configured to process the mismatch. For example, a 2-channel input is provided to a stereo audio player that is connected to left and right speakers and a subwoofer. A mismatch between the input and the output configuration would manifest as no sound comes out of the subwoofer. Likewise, a 3-channel input is provided to an audio player that is connected to only left and right speakers, the mismatch between the input and the output configuration would cause lacking of bass or low frequencies sound when the stereo audio player assumes a subwoofer exists, but in fact it is not.
On the input side, detecting the source format or configuration is relatively easy, especially when the source is in digital format (i.e., from the audio data encoding scheme). On the output side, the industry standard passive speaker interconnects do not support auto-discovery or speaker device interrogation. To solve this problem, today's audio players often require intervention from a user to set a given configuration or predetermined output configuration. For example, there may be a physical switch that enables or disables a subwoofer or a set of predetermined output patterns provided by an audio player for a user to connect the audio player to corresponding speakers or a subwoofer if there is one. While the current solution may be satisfactory, it is, however, inconvenient and confusing for many users who are not skilled in the audio field.
There is, therefore, a need for solutions in stereo audio players to automatically convert an input audio source properly to match physical audio output speakers based upon detection of the physical output speakers, especially the presence of a subwoofer.